Vaccines that target tumor self-antigens require a deeper understanding of the mechanisms of peripheral immunologic tolerance. Much is understood about tolerance induction by CD4+ T regulatory (Treg) cells, but suppression associated with undefined unique CD8+ T cells in cancer is understudied. A gap in the knowledge of how undefined CD8+ T cells suppress immunity to tumor self-antigens and of what defining markers they express are obstacles preventing progress for cancer vaccine development. This gap represents an important problem because, until it is filled, developing the best vaccine strategy against tumor self-antigens may not be possible. Our goals and objectives for this project will overcome this obstacle by first, identifying the mechanism(s) used by a unique subset of CD8+ T cells to suppress immunity to the tumor self-antigen TP (D52), and second by defining new phenotypic markers on these unique suppressor CD8+ T cells elicited by vaccination against over expressed tumor self-proteins modeled by D52. Our hypothesis is that a unique subset of CD8+ T cells is elicited by D52-vaccination and actively participates in suppressing immunity to this overexpressed tumor self-oncoantigen. This hypothesis was formulated on the basis of preliminary data produced in our laboratory. The rationale for the proposed research is that vaccination against murine D52 tumor self-protein (mD52) to prevent tumor growth in murine models of cancer results in partial tumor immunity that requires the generation of mD52-specific CD4+ and CD8+ IFN-? secreting T cells. However, a unique sub-population of CD8+ T cells that secrete IL-10 only is also elicited with CD4+Tregs and may be playing a role in suppressing tumor immunity. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Determine the function of the CD8+ IL-10+ T cells elicited by mD52-vaccination; 2) Identify defining marker(s) on the CD8+ IL-10+ T cells elicited by mD52-vaccination. Under the first aim, CD8+ IL-10+ T cells will be isolated from mD52-vaccinated mice and their mechanisms of immune suppression analyzed. In the second aim, cell-based markers for definitive characterization of these unique CD8+ IL-10+ T cells will be identified as a critical step for translating D52 vaccination strategies clinically as a combination therapy. This proposal is innovative, as it focuses on a unique subset of CD8+ T cells elicited by vaccination against an understudied, relevantly overexpressed tumor self-oncoantigen shared by a wide variety of cancers. We are uniquely poised to successfully carry out this work because we co-discovered D52 and demonstrated its potential as a vaccine. The proposed research is significant as it is expected to vertically advance and expand understanding of how to best overcome challenges related to immunologic tolerance to tumor-self antigens not addressed by other well-studied processes of immune regulation. The results should support development of more effective vaccines against other shared, over expressed tumor self-antigens, in addition to D52.